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Saturday, July 30, 2011

Stictoporellina sp. was the first recognizable Bryozoan I found within the rocks of the Verulam formation of Ontario. It's distinct enough to spot without having to rely on thin sections and microscopic analysis of them. It kind of looks like a chain link fence to me but with lots of little pores called zooids.

This specimen appears to have parts of the colony enveloping some rounded openings. Were these perhaps where soft bodied worms lived?

Yet another specimen...

You can see another specimen of this Bryozoan that I posted in an earlier entry by clicking here.

Thursday, July 28, 2011

For a while I was confused by these broken bits of coral, that I frequently found at Arkona, and called them Alveolites goldfussi.

My friend Joe K. pointed out to me that Alveolites generally does not form branching structures but Cladopora does. I am now labeling these pieces as Cladopora roemeri as that is the most common species found within the Hungry Hollow member of the Widder formation. Besides the branching structure of the coral the calices, where they individual polyps lived, are shaped like little triangles (or sometimes I call them "fish scales".

There are many species of this coral and some were once referred to as "Coenites". Here is a piece that shows evidence of branching.

Most of the Cladopora that is found within the Hungry Hollow member of the Widder formation, which is Middle Devonian (Givetian) in age, at Arkona are small, inch or so sized pieces that have eroded out of the rocks. To find larger specimens you need to search for them still embedded within the matrix.

Joe K. managed to extract a large set of branches from matrix and reassemble them into life position as can be seen here.

Tuesday, July 26, 2011

In 2009 I was able to visit a site that had tantalized me as a youth, the fossil beds near Farson, WY. They were a part of the same Eocene lake system that formed the Green River Formation and contain the same fauna (fish mainly) that can be found at the famous quarries near Kemmerer. The difference is the rock which is a very fine grained shaley limestone as opposed to the pure limestone found farther east in Kemmerer. This is a piece I bought years ago that came from the Farson locality. It features a large number of Knightia sp. fish all grouped together in what is called a mortality plate. The fish were all killed at the same time possibly by water temperature changes or sudden drops in the amount of dissolved oxygen.

Notice how the fish are very finely detailed and stand out from the rock.

The site is out in the vast plains of the Sweetwater Valley north of the town of Green River. As I was driving to the site I was expecting small quarries like those in Kemmerer but what I found was a relatively flat featureless plain spotted with Sage.

It looked to me that things had been confined to small scale digging in the immediate surface layers as evidenced by the large amount of scattered rock slabs. The heyday of this site was in the 50's to 70's before the government came in and put a ban on collecting vertebrate fossils on federal land. The site is in the middle of a vast area of BLM (Bureau of Land Management) jurisdiction so no collecting for me.

I poked around a little in the old, weathered slab piles to see if I could find anything that had been cast off and did find a few bits.

This was probably the best piece that I found. I like the contrast of the rock's patina with the partial fish fossil.

I left the pieces I'd found and had to be content with the pictures I had taken. It's too bad they don't allow collecting here but if it were otherwise it culd be overrun and depleted by commercial collectors very quickly.

Sunday, July 24, 2011

The Silurian aged Waldron shale preserves an odd fossil that looks like the roots of a plant (like a bush or tree) but they actually belong to a Crinoid which is an animal. These roots are the holdfast of the crinoid which is at the opposite end of the stem from the calyx and is what it uses to attach itself to the sea floor.

Here is a classic example of this interesting fossil showing a dendritic pattern to the roots. There is also a partial Eucalyptocrinus calyx on the right hand side.

This specimen has some Pyrite crystals that have grown on the fossil and a cluster of bladed crystals near the end of one root that I think are Marcasite.

These are good examples of this unusual method that Crinoids employ to keep themselves stable in the currents. Some crinoids attach to a hard surface like a shell or coral with a warty growth while others are more free floating or mobile. These "root" systems likely developed because the substrate of the sea floor was very soft and muddy and did not provide many hard attachment points.

Friday, July 22, 2011

I was going through pictures I took a few years back while visiting Capitol Reef National Park in Utah and found this image of the Jurassic aged Navajo Sandstone.

It's the wall of a narrow slot canyon and you can see cross bedding which has been interpreted as fossil sand dunes. I especially like the disconformity that is present as is seen by the angle of the layers in the bottom half versus those in the top half. Essentially what this is showing is that the lower half formed as a set of sand dunes that became cemented (probably during a wetter interval). The cemented dunes later was eroded down to a relatively flat surface and then another set of dunes formed on top. The Navajo sandstone is interpreted to represent sand dunes that formed in a dry, arid climate such as a desert. The modern analog would be the Sahara Desert of western Africa.

Here are some more pictures of the rock formations that I saw during my visit.

Formations such as these are what give the park it's name as the near white sandstone erodes into rounded shapes similar to the dome of the Capitol building in Washington D.C.

This is a typical slot canyon. Narrow, high walled and nowhere to go if a flash flood comes along.

Evidence that is was not always hot and dry can be seen in ripple marks preserved in sandstone.

Monday, July 18, 2011

This is an interesting piece of matrix from the Centerfield member of the Ludlowville formation that I found near East Bethany, NY. It has a rugose coral, likely Heliophyllum, that colonized a fallen branch of Favosites sp.

A closer view of the Favosites and you can see an eye and partial cephalon of a Phacops on the left side of the picture.

You can clearly see that the horn coral originates in one of the vacant cells on the branch of the Favosites. I like all the twists and turns that the calice of the Heliophyllum takes as it grew.

The Centerfield member of the Ludlowville formation represents a period of lower sedimentation, and possibly higher sea levels, which allowed the coral fauna to prosper. It corresponds to the Hungry Hollow member of the Widder formation in Canada and has been correlated to a section of the Mahantango formation, in Pennsylvania, called the Centerfield coral reef.

Saturday, July 16, 2011

Favosites placenta argus (edit 02/02/14) is an easily recognizable species in the field. It's a tabulate coral and forms flat, plate like colonies. The surface of the colony is covered with small calices where the animals would have lived as is typical for this genera. The feature that distinguishes it from other species of Favosites is that the calices vary in size and shape.

Here is a typical small colony that I found in the Hungry Hollow member of the Widder Formation (Middle Devonian) at Arkona.

Note the flat, wavy look to the underside of the colony. This was the result of it's position on the soft sea floor and subsequent spreading.

The calices of Favosites placenta vary in size but always have a pattern of large round shapes surrounded by smaller angled shapes.

Tabulate corals grew by cloning so all individuals of a colony would essentially be the same critter. They would spread by dividing or "budding". Maybe the larger calices represent more mature animals and the smaller calices are the divisions?

Thursday, July 14, 2011

Favosites is an ubiquitous tabulate coral in the Paleozoic. Often it was the primary reef building coral and as such there are many different species. The specimen below is one called Favosites alpenensis. It forms large colonies that are often flattened and disc shaped but covered with the typical hexagon shaped cells reminiscent of a honeycomb.

These colonies can grow to be quite large. At my friend Joe K.'s house he has one in his garden that is easily four to five feet across. Here is another that appears to have vertical growth but I think it actually represents several periods of recolonization after burial. Note the uneven layering and exposed side walls to some of the cells. I think that the exposed walls are merely an expression of the corals growth in the soft sediment that surrounded it.

Please note that the above specimens came from the Hungry Hollow member of the Widder formation, Middle Devonian (Givetian) in age and were collected near Arkona, Canada. I've been told that Favosites alpenensis is a species that is "specific" to the rock formations around Alpena, Michigan. Within my collection I'm going to keep the Favosites alpenensis name until such a time as I find evidence that is is otherwise named. Such are the difficulties inherent with labeling fossils from different localities or, in this case, countries.

About Me

I'm a 40-something, life long student of Geology living in Philadelphia. My interests include Photography, Architecture and History among other things. When not cleaning my recent finds you'll find me in my backyard Hybridizing Daylilies or working in my garden. This Blog is an outlet for me to express my interest in fossils, catalog my collection and coalesce my thoughts and research into a useful medium.